The present invention relates a method of manufacturing a lead frame used in an electronic component such as an IC (integrated circuit), or an LSI (large scale integration).
In general, electronic components such as an IC and an LSI have been widely known. Also, in a conventional lead frame, as shown in FIG. 10, an island portion "C" used for mounting a semiconductor chip "B" is integrally formed in one body on a lead frame "A" made of a thin metal plate, a large number of lead terminals "D" whose widths are made narrow are integrally formed in one body in such a manner that an inner lead "D.sub.1 " positioned at a tip portion of the respective lead terminals "D" is extended in a radial direction toward the island portion "C". These inner leads "D.sub.1 " positioned at the tip portions of the respective lead terminals "D" are mutually connected with the above-described semiconductor chip "B" by using very fine gold wires "E" by way of a wire bonding process, and thereafter the entire components are packaged by a mold unit made of a synthetic resin.
Recently, there is extremely increased the number of lead terminals owned by electronic components, for instance, ICs and LSIs, which are manufactured in high integration. To increase the total number of lead terminals without making these electronic components bulky, the width size "W.sub.1 " of the inner lead D.sub.1 at the tip portion of the respective lead terminals "D" must be narrowed and also the pitch interval "P" between the adjoining inner leads "D.sub.1 " must be shortened. In case that these lead terminals are formed from a thin metal plate by a conventional punching process or the conventional etching process, both of the width size "W.sub.1 " of the each inner lead at the tip portion of the respective lead terminals and the interval dimension "W.sub.2 " between the adjoining inner leads cannot be reduced less than 80% of the thickness of this metal lead frame.
Conventionally, the width size W of the inner lead D.sub.1 of the respective lead terminals is narrowed and also the pitch interval "P" between the adjoining inner leads "D.sub.1 " is narrowed by making the thickness of a raw metal plate "A" thinner, which is used for the lead frame. However, when the thickness of the metal plate used for the lead frame "A" is made thinner, the thickness of the entire lead terminal "D" becomes thinner, so that strength of outer lead portion of the lead terminal "D", which projects from the mold portion, is lowered. As a result, since the thin outer lead portion is extremely apt to be deformed, there is a limitation in increasing the degree of integration of an electronic component by making the thickness of the lead frame "A" thin. In other words, there is a problem that provision of a large number of lead terminals may cause a bulky electronic component.